The pouring and use of concrete is a fundamental construction task in the trade. It is referred to as the placement of concrete. It is often required in the installation of sidewalks. It is placed over steel decks to provide the flooring base for multi-story skyscrapers; it is placed for the flooring of large warehouse or industrial structures; and it is placed to form the basis for water retention basins and reservoirs. It further pro vides the basis for highway surfaces and airport runways.
There are two essential joints associated with concrete slabs. The first joint is commonly referred to as the expansion joint and passes completely through the concrete slab. The expansion joint is designed to allow for the expansion and contraction of the concrete slab in response to ambient temperature conditions. The second joint is commonly referred to as the control joint. The control joint is a linear impression formed in the concrete slab after its placement. It does not extend through the concrete slab. The purpose of the control joint is to control the direction of any cracking which may appear in the slab over time. Typical control joints would run transversely on the slab from one edge to the other. Control joints would normally be formed by dragging a trowel across the poured concrete while it is still wet to form the linear impression, and in some instances, diamond saws would be used to form the control joints after the concrete slab had hardened.
In the prior art, any handy material would be utilized to form the peripheral outline or frame of the concrete slab and any associated expansion joints. The concrete would be placed within the frame and leveled using a screed which would be dragged across the surface of the wet concrete while resting on at least two adjacent or abutting framing members in order to achieve a planar level slab. The framing members upon which the screed rested while leveling the surface of the concrete slab are referred to in the trade as screed guides.
European building codes require a ten year guarantee with respect to poured concrete slabs. No such guarantee is required or exists in US building codes. This dichotomy has led to greater technical advances in Europe with respect to the pouring of concrete slabs. In particular, a screed guide profile has been developed in which the screed guide itself also forms the control joint for the concrete slab. The use of these combination screed guide/control joints presents some great advantages in the area of placement of concrete slabs and in the life expectancy of the concrete slabs. However, the accurate placement of the screed guide/control joints has in some cases proved laborious and time consuming.
Initially, some screed guide/control joints were positioned by pouring small mounds of concrete in a desired linear direction before positioning of the screed guide/control joint. The screed guide/control joint would then be positioned on the small mounds of concrete to the desired height, and the mounds of concrete would be allowed to set. Once the mounds of concrete had set, securing the screed guide/control joint, the concrete slab would be poured to the height of the upper edge of the screed guide/control joint. This method became laborious and time consuming since normally 24 hours would have to elapse from the time that the mounds of concrete were poured until the time that the slab could be poured to allow for the mounds to set and position the screed guide/control joint.
The method of installing screed guide/control joints evolved to the use of rebar stakes, and clips. The section of rebar would be pounded into the ground to an estimated height, each rebar being positioned approximately two feet apart. Clips would then be installed on the top of the rebar, the upper portion of such clips presenting a dove tail channel into which a preformed plastic screed guide/control joints having a pyramidal cross section which would snap fit. The worker would hand adjust the depth of the rebar in order that the clips were at the same height so that the screed guide/control joint presented a level upper edge for placement of the concrete slab. This method presents problems when a vapor barrier is utilized, since the rebar stakes will pierce the plastic sheets or other types of vapor barriers and degrade their performance. It also presents a problem when concrete flooring is being placed on a steel deck as is done in the construction of multi-story buildings or skyscrapers. The rebar stake cannot be driven into or through the steel deck.
It presents an additional problem in those instances where concrete slabs are being placed onto compacted gravel sub grade or ground. Some installations call for void forms to be placed beneath the concrete slab at various locations to compensate for the expansion and contraction of the ground due to expansion and contracting soil conditions. These voided areas are formed utilizing cardboard housings which are positioned prior to the placement of the concrete slab, the slab being placed essentially over the cardboard encapsulating the cardboard housing between the concrete and the ground. The void area under the cardboard housing and in contact with the ground provides compensation for expansion and contraction of the ground. The cardboard housing over time will eventually deteriorate, but the void will remain. The use of the rebar stakes or any stake on such a slab would pierce the cardboard housing and obviate its desired purpose of forming a void between the poured concrete and the ground.
An additional problem associated with the current installation of screed guide/control joints is that the profile of the screed guide/control joint varies depending on the thickness of the concrete slab. Two sizes of screed guide/control joint profiles are currently used for screed guide/control joint placement in various thicknesses of concrete slabs. A large profile screed guide/control joint is utilized for placement of six inches or greater, and a small profile screed guide/control joint is used for placements of lesser thickness. Since the size of the screed guide/control joints vary, the installer must inventory a quantity of clips that will fit the two profiles.
This screed guide profile and its advantages would find greater acceptance both in Europe and the US if the aforesaid disadvantages could be overcome. The system of the present invention addresses and overcomes each of these disadvantages.